Back in the day there was only one putty to use--Testors. I remember it came in a grey tube, and sadly would not work as a substitute for glue (although my brother and I tried this when we ran out of Testors "Stinky Red" glue a couple of times).
Thirty years later there are more choices, and over the past year or so I've been trying to improve my ability to use putties to fill and customize model kits, just as I did as a youngster. I had forgotten how hard getting a good, smooth finish with plastic fillers can be....but after some reading and trial and error I'm improving....and can do things faster now which is always good.
For this week's build I need to fill some 1/16" deep cavities on the back of the body (Revell 55 Chevy #85-2069) of a 55 Chevy Gasser. On the stock kit the Revell tooling guys had dug out channels to accommodate the side molding strips. It's cool that Revell did this; it's easier to use premade chrome strips off the parts tree than try to use bare metal foil to get that "brightwork" look. But no C/GS drag racer in his right mind would have left trim in place on a 1:1 gasser; it's extra weight that's not needed, and looks a bit "pristine". So off they go.
Well, not so fast. Filling in 3.5" long and 1/16" deep channels that run the length of the rear of the body, are curved and oddly contoured, isn't that easy.
So here is my current thinking. First, always fill in as empty space as possible with plastic before doing anything else, so I used some Evergreen strips.
Next I laid in the first round of putty--Tamiya Basic Putty is what I've been using lately. This is straightforward; I just apply some where needed, right out of the tube, mold it with a toothpick, and let it dry for a couple of days.
When it comes time to sand out the dried putty things get a bit more interesting. As far as I can tell you MUST use something between your hand and the sandpaper to have your putty work sand out OK. I read this in two hobby books (so it must be true, right?) and first tried little blocks of balsa as my "scale sanding block", which was better than nothing, but not much. Not believing what I had read I went back to using wet sand paper applied directly to the custom body work....but it took forever to sand out and never seemed to get things completely smooth.
After trying different things I ended up changing materials for my "sanding block". That did the trick. The best block I found so far is a tiny hunk of foam rubber. What you see here was cut off a big hunk that came with a computer part I got at work. I wrap the sandpaper around the foam rubber, and then dip the whole thing in water with a bit of dish soap. I am not sure why this makes as big a difference as it does, but it's a HUGE advantage to sand this way--you gain about 100x the "sanding power". What might have an hour of sanding takes maybe 10-15 minutes. And the resulting body work comes out much smoother than if you don't use the foam rubber "buffer".
I have found that the first batch of puttying always leaves tiny holes and imperfections, no matter how carefully I try to sand it. So the "finishing" step is to prime the body (I use Duplicolor Primer/Sealer, straight out of the rattle can, but I imagine any sort of primer that isn't enamel based will work fine) then use dabs of Model Masters red putty mixed with Testors liquid cement brushed over. The liquid cement thins the putty out and makes it easier to spread around. The touch up putty dries quickly and is ready to sand in a couple of hours. I sand it again (usually using 400 to 600 grit wet and dry) using the "foam block" method.
The result is this cool patchwork sort of look. What you see here is almost ready to go--I will prime it again to see what else I have to do, but it's looking like it's getting close.